popwatcher

popwatcher is a daemon that maintains a list of hosts that are
authorized to use your mailserver as an SMTP relay based on those
hosts successfully authenticating to your POP mail server. The default
configuration is designed to work with qpopper and exim, but can be
used with other mailers and POP servers.

Recent comments

compared to popaccess
I am the author of popaccess (also on freshmeat), which I wrote for which seems many of the same reasons you did, as a replacement for popauthd. I am just courious if you knew about it before you started popwatcher? I was just courious what the differences between the two are. Perhaps we can join efforts do avoid what seems like a lot of duplicate work.